Ferroelectric materials are well known. They are usually crystalline substances which have a permanent spontaneous electric polarization (electric dipole moment per cubic centimeter) that can be reversed by an electric field. See, e.g., pages 239-242 of Volume 5 of the "McGraw-Hill Encylopedia of Science and Technology,"(McGraw-Hill Book Company, New York, 1977), the disclosure of which is hereby incorported by reference into this specification.
Ferroelectric materials have found many uses. The piezoelectric effect of ferroelectrics finds numerous applications in electromechanical transducers. The large electrooptical effect (birefringence induced by an electric field) is used in light modulators. In certain ferroelectrics, light can induce changes of the refractive indices; these substances can be used for optical information storage and in real-time optical processors. The temperature dependence of the spontaneous polarization corresponds to a strong pyroelectric effect which can be exploited in thermal and infrared sensors. The high dielectric constants of these materials allows them to be used as dielectrics.
A ferroelectric material in fiber form could be used for many purposes. Thus, they may be used to prepare composites with polymers such as, e.g., epoxies, polyurethane, and the like; these composites may be used for piezoelectric, pyroelectric, electrooptic, and dielectric applications. Thus, e.g., they may be used in in-line fiber optic devices such as, e.g., devices for harmonic generation, electrooptic modulation, and the like. These fibers may be used in acoustic and acoustoopic devices. They may also be used a sensors; they can be chemically doped to make them semiconducting with dopants such as, e.g., iron, tungsten, manganese, yttrium, niobium and the like.
In a publication in April of 1989, by S. Hirano et al., entitled "Preparation of Stoichiometric Crystalline Lithium Niobate Fibers by Sol-Gel Processing with Metal Alkoxides," J. Amer. Ceram. Soc., 72[4] 707-709(1989), the preparation of sintered polycrystalline lithium niobate fibers was disclosed. Applicant invented his polycrystalline, ferroelectric fibers prior to April of 1989.
It is an object of this invention to provide a polycrystalline, ferroelectric fiber.